Organic pigment and/or inorganic pigment are widely used in paint, ink and the like in general, for such purposes as favorable appearance, light-shading, rust-proofing and the like. When these pigments are used in paint, however, in occasions the pigments fail to be uniformly dispersed in the paint to invite inferior appearance or water resistance of the resulting coating film of the paint, which has been a problem requiring a solution.
For example, JP Hei 6 (1994)-211944A discloses that a pigment-dispersing resin formed of a copolymer (A) of (meth)acrylate having C1-4 alkyl group, (meth)acrylate having C6-30 alkyl group and polymerizable monomer having a specific structure, excels in pigment-dispersing ability of various pigments and exhibits good compatibility with various resins used for paints, while being free of such problem as weatherability. However, when the pigment-dispersing resin is used in paint, coating film formed therefrom may show inferior water resistance.
JP 2001-2736A discloses that the use of a pigment-dispersing acrylic resin having a weight-average molecular weight within a range of 10,000-100,000, which is obtained by copolymerization of a monomeric mixture comprising a polymerizable unsaturated monomer containing at least one of hydrophilic functional group selected from amino group, quaternary ammonium salt group and sulfonic acid group; hydroxyl-containing polymerizable unsaturated monomer; (meth)acrylic acid ester monomer of a specific structure having C8-24 branched alkyl group; and other polymerizable unsaturated monomer can provide a pigment-dispersing paste composition of which pigment-dispersibility, let down stability and the like are drastically improved. When the pigment-dispersing resin is used in paint, however, resulting coating film may exhibit inferior water resistance.